The present invention relates generally to a disk drive having a load/unload ramp, and in particular to improvements in the load/unload ramp.
FIG. 1 shows a plan view of a typical disk drive having a single disk 8 that spins between two head suspension assemblies 24A, 24B (only one head suspension assembly 24A is visible). To access different data tracks, the head suspension assemblies are moved by an actuator arm 25 in the radial direction of the disk. The actuator arm 25 is turned on a shaft 21 by a voice coil motor, as described later.
As shown in FIG. 2, each head suspension assembly comprises a load beam 26A (26B) attached to the actuator arm 25, a tab 28A (28B) located at the tip of the load beam, a flexure 30A (30B) attached to the load beam, a slider 11A (11B) attached to the flexure, and a read/write head 12A (12B) attached to the slider. The flexure is a delicate structure that allows the slider to pitch and roll against a dimple (not visible) in the load beam, in compliance with the disk surface, for proper air-bearing performance as the slider flies above the spinning disk.
The load/unload (LUL) ramp 40 in FIG. 1 provides a safe place to park the head suspension assemblies when the disk is not spinning, to prevent contact between the sliders and the surface of the stationary disk.
FIG. 3 shows a sectional view of a conventional LUL ramp 40, also showing the outer edge of the disk 8 with the sliders 11A, 11B and tabs 28A, 28B. The flexures have been omitted for simplicity.
To unload the sliders from the disk, the load beams move to the right in FIG. 3. The load-beam tabs 28A, 28B land on inclined lifting slopes 44 at the front of the LUL ramp and travel up the lifting slopes, across maximum lift surfaces 46, and down back slopes 48 to reach parking surfaces 50, as indicated by the dotted arrows. As the tabs 28A, 28B ascend the lifting slopes, the sliders 11A, 11B are lifted away from the disk 8. When the sliders are loaded onto the disk, the above motions are performed in reverse.
The lifting slopes 44 must be high enough to allow for variations in the landing point of the load-beam tabs, and to provide at least a minimum necessary lift in the worst case. The inclination of the lifting slopes must be sufficiently gradual that the sliders do not approach the surface of the disk too rapidly when being loaded. The back slopes 48 must be high enough to prevent unintended escape of the load-beam tabs from the parking surfaces 50. In a disk drive with a small form factor, to minimize the dimensions of the LUL ramp, the lifting slopes 44 are generally made as low, short, and steep as possible within these constraints. Minimizing the height of the lifting slopes 44 has the added advantage of minimizing the energy needed to unload and park the sliders. A conventional LUL ramp is symmetric with respect to the median plane 7 of the disk 8; both lifting slopes 44 have the same minimum height and maximum inclination, and in the parked position, the sliders are separated by a distance comparable to the thickness of the disk.
A problem is that the flexure design characteristics that allow the sliders to pitch and roll while flying over the disk also allow the sliders to pitch and roll in their parked position. Violent pitching and rolling motions can occur in response to shock forces, as when the disk drive is dropped. To aggravate the problem, since the flexures are only lightly loaded against the load-beam dimples, shock forces can easily separate the flexures from the dimples, allowing the sliders to come closer together. Thus while the sliders cannot contact the disk surface in their parked positions, which are outside the disk perimeter, the parked sliders can collide with each other. Such collisions can damage the air-bearing surfaces of the sliders, possibly rendering the disk drive inoperable.
To prevent such collisions, U.S. Pat. No. 6,067,209, filed Jun. 17, 1998 by A. Aoyagi, D. W. Albrecht (the present inventor) and others, provides the LUL ramp with limiter surfaces that interact with tab-like extensions of the flexures. The limiter surfaces restrict the movement of the flexures in the parked position, as will be described later. For complete collision prevention, a separator plate can also be inserted between the sliders.
However, because of the continuing reduction in disk drive dimensions, including disk diameter, disk drive thickness, and disk thickness, the separation between the parked sliders is becoming very small. For instance, in a disk drive which is currently envisaged, the thickness of the disk is on the order of 0.4 to 0.6 mm, and the distance between the parked sliders is on the same order. With such a narrow separation, the sliders may collide during shock events despite the above-mentioned limiter surfaces. If a separation plate is inserted, then instead of colliding with each other, the sliders may become contaminated by contact with the separation plate, leading to contamination of the disk surface, again with adverse effects on air-bearing performance.
In this connection, it should be noted that disk drives of a very small size are likely to be used in handheld devices, such as digital cameras. In these applications, the disk drive will often be a removable storage unit, which is apt to be roughly handled or dropped, and therefore experience severe shock forces.